Radio communication systems are known to include a multitude of communication units vying for a limited number of communication resources. The communication unit, which may be a mobile radio, a portable radio, or a dispatch console station, transmits service requests when the need arises to use a communication resource. Such services include, but are not limited to, private calls, talk group calls, interconnect calls, and dispatch calls. As is known, when a communication resource of the type being requested is available, a controller (such as a central controller) assigns an available communication resource to the requesting communication unit. At that time, the communication unit engages in the desired communication.
The users of such communication units are typically organized in talkgroups. Talkgroups often represent users that share a common mission, much like a workgroup. Such talkgroups can be rendered less effective, however, if substantially all services are not available at all times to all talkgroup members.
Numerous wireless system types exist to provide such communications. These systems often provide communication over a wide geographic region through the use of multiple base station radio sites, commonly known as cell sites. Generally, these wireless systems are limited to some maximum number of cell sites as a function of many factors, including switching center hardware limitations of the switching and call control equipment.
There is a growing trend among the users of these wireless communication systems to communicate with each other over larger geographic areas, thus urging the radio systems to extend their geographic coverage. Many of these wireless communication systems can be coupled to each other when they are of the same system type to provide the users with a composite larger system and hence an extended geographic operational area. It can be costly, however, to expand a wireless communication system in this manner, especially if the requirement for coverage in some geographic regions is minimal.
Furthermore, many times there is an existing installed base of varying types of wireless communication systems that can provide acceptable communication service within parts of the desired composite coverage area. Multi-mode communication units exist that support communication in a variety of modes (one at a time), such as either analog or digital wireless communication. The desire of talkgroup communication unit users to consistently share the same communication services, however, is often not met when they operate from varying wireless communication system types. For example, talkgroup members split between two or more wireless communication system types may not be able to communicate with each other, and when they can, often only the most basic communication services are supported as the system external interfaces often support only the simplest communication services.
One way to join two or more wireless communication systems is to use a dispatch console system cross patch. While this may provide some basic cross system communication, it is usually associated with many limitations, including missed calls (since channel resource non-availability is generally not a factor considered in the patch logic), limited audio quality (due to the transformation of speech signals from a first digital format into analog and then into a second digital format), and missed speech (resulting from the slow speed of establishing a patched communication path).
Accordingly, a need exists to provide enhanced connectivity as between a first wireless communication system of a first type and at least a second wireless communication system of a second type that avoids the shortcomings of the prior art. In particular, a method and apparatus that permits a communication unit to operate from a different system type with other members in a same talkgroup without undue missed speech, missed calls, limited audio quality, and other compromises would represent a significant improvement.